Phase Transitions and Virtual Exceptional Points in Quantum Emitters Coupled to Dissipative Baths

TL;DR

This paper explores how dissipative environments influence quantum emitter relaxation, revealing phase transitions and virtual exceptional points that can be harnessed for quantum control and dissipation engineering.

Contribution

It uncovers the existence of dynamical phase transitions and virtual exceptional points in a quantum emitter coupled to a dissipative bath, linking NH spectral restructuring to emitter dynamics.

Findings

Identification of dynamical phase transitions in emission decay

Discovery of virtual exceptional points governing spectral coalescence

Optimal dissipation conditions for accelerated emission

Abstract

Controlling atom-photon interactions in engineered environments is central to quantum optics and emerging quantum technologies. Non-Hermitian (NH) photonic baths, where dissipation fundamentally reshapes spectral and dynamical properties, provide versatile platforms for such control. Here we investigate the relaxation dynamics of a single two-level quantum emitter coupled to the edge of a semi-infinite dissipative bosonic lattice with uniform loss. Despite the simplicity of this bath, we uncover rich dynamical phase transitions, i.e. qualitative changes in spontaneous emission decay as system parameters are varied. In particular, we establish the existence of an optimal dissipative environment for accelerated spontaneous emission. The phase transitions are traced to spectral restructuring of the resolvent, in some cases governed by the coalescence of resonance states on the second Riemann sheet. We identify these coalescences as virtual exceptional points (EPs) of resonance origin, providing a conceptual bridge with EP physics while highlighting distinctive features of infinite-dimensional NH systems. More broadly, our results illustrate how the specific nature of dissipation -- whether uniform losses, staggered losses, or dephasing -- can profoundly impact emitter relaxation, pointing to dissipation engineering as a versatile tool for quantum technologies.